The present invention pertains to polyolefin compositions containing a stabilizer or mixture of stabilizers selected from the group consisting of the phenolic antioxidants, the hindered amine light stabilizers, the ultraviolet light absorbers, the organic phosphorus compounds, the alkaline metal salts of fatty acids and the thiosynergists, which are stabilized against degradation and/or discoloration by an effective amount of N,N-dibenzylhydroxylamine or other selected hydroxylamine derivative.
Although phenolic antioxidants have long been known to be very effective stabilizers for polyolefins and have enjoyed wide commercial success for that use, polyolefin compositions stabilized with phenolic antioxidants tend to discolor upon heating at elevated temperatures for prolonged periods or upon exposure to the combustion products of natural gas.
While the concomitant addition of organic phosphites to such polyolefin compositions mitigates the discoloration, it remains a serious practical problem.
Likewise polyolefin compositions containing certain phenolic antioxidants and hindered amine light stabilizers tend to discolor upon storage for extended periods even at ambient temperatures.
The organic hydroxylamine compounds, such as N,N-dibenzylhydroxylamine, are generally known and some are commercially available.
U.S. Pat. Nos. 3,644,278 and 3,778,464 describe the use of substituted hydroxylamines of varying structures as antioxidant stabilizers for hydrocarbons including polyolefins. The use of such substituted hydroxylamines in polyolefins in combination with a phenolic antioxidant or in combination with an organic phosphorus compound, an ultraviolet light absorber, a thiosynergist or a hindered amine light stabilizer with the resulting resistance to degradation and/or discoloration is not disclosed or suggested.
U.S. Pat. No. 3,408,422 discloses the use of selected hydroxlamine derivatives in unsaturated polyester compositions to prevent premature gelation on storage.
U.S. Pat. No. 3,926,909 describes the use of substituted hydroxylamines as stabilizers to prevent the discoloration of polyurethanes (spandex) upon exposure to light, smog or gas fumes.
U.S. Pat. No. 4,242,224 discloses that the pink discoloration which occurs in the amine antioxidant and antiozonant emulsions used in the latex industry at high pH values can be prevented or retarded by the use of dialkylhydroxylamine or mercaptan stabilizers.
U.S. Pat. No. 4,316,996 pertains to a process of preparing phenolic antioxidants in the presence of a hydroxylamine derivative and of a substituted oxime to yield a phenolic antioxidant which itself exhibits improved color and color stability. It is stated that, when such antioxidants are incorporated into rubber, the amount and rate of discoloration is reduced. The instant compositions are not disclosed or suggested.
U.S. Pat. No. 3,432,578 relates to conjugated diene polymer compositions stabilized against the adverse effects of ultraviolet light by use of diaryl or diaralkyl hydroxylamine compounds including N,N-dibenzylhydroxylamine. It is noted that the dialkylhydroxylamines are completely ineffective in stabilizing such polymer compositions. This patent mentions that other stabilizers may be used in conjunction with the hydroxylamine derivative and in Table I discloses stabilized compositions consisting of a conjugated diene polymer, phenolic antioxidants and N,N-dibenzylhydoxylamine. Such compositions were resistant to decomposition upon ultraviolet exposure.
U.S. Pat. No. 4,386,224 discloses the use of N,N-diethylhydroxylamine as a color stabilizer for monoalkyl phenols such as nonyl or dodecyl phenol.